The utopia may be usefully contrasted with the dystopia.
Examples of utopias:
The section in Gulliver's Travels by Jonathan Swift depicting the calm, rational society of the Houyhnhms, is certainly utopian, but it is meant to contrast with that of the yahoos, who represent the worst that the human race can do.
[Looking Backward]?, by Edward Bellamy
[News from Nowhere]?, by William Morris; see also the [Arts and Crafts Movement]? founded to put his ideas into practice
A large number of books by H.G. Wells
Aldous Huxleys book Island?. (His most famous work, [Brave New World]? could perhaps be considered a utopia, as the people in that society are certainly happy, but it is more generally regarded by critics as a dystopian satire, as they actually have no choice in whether they are happy or not.)
[B.F. Skinner]?'s [Walden Two]?
The Dispossessed, a science fiction novel by Ursual K. le Guin. sometimes said to represent one of the few modern revivals of the utopian genre, though it is notable that one of the major themes of the work is the ambiguity of different notions of utopia.